Double wall exhaust pipe

ABSTRACT

A double wall exhaust pipe comprising inner and outer conduits includes a plurality of inwardly lanced strips on the inner conduit which are reformed to their original position. The lanced strips yield upon pressure buildup between the conduits to allow pressure venting while maintaining a double wall thickness resistance to corrosion.

United States Patent Keller Sept. 17, 1974 DOUBLE WALL EXHAUST PIPE2,941,544 6/1960 Perus 137/5251 x 3,382,948 5/1968 W lk t 1 181/35 B[75] Inventor: Robert Keller, Troy Mlch- 3,572,379 3/1971 Pozai t alf137 5251 [73] Assignee: General Motors Corporation,

Detroit, Mich. Primary Examiner-Richard C. Queisser AssistantExaminerDaniel M. Yasich [22] Flled' 3; 2 1972 Attorney, Agent, orFirm-Peter D. Sachtjen [21] Appl. No.2 3 ,4 1

[57] ABSTRACT [52] US. Cl. 138/178, 137/525.1, 181/36 B 51 1111.01. F1619/18 A duble exhaust compr'smg and 58 Field 01 Search 138/178, 177, 140,143; P 9999919mcludeseplurality inwardly lance? 137/525'1; 181/35 B, 36B strlps on the 1 nner condu1t WhlCh are reformed to then origmalposmon. The lanced strips yleld upon pressure [561 2:;wtlirzziztatxzgzfizizzrs 3291121 225: :23;-

UNITED STATES PATENTS tance to corroslon. 2,386,747 10/1945 Ris 138/140X 2,808,896 10/1957 Wilman 181/36 B 2 Claims, 7 Drawing Figures 1 DOUBLEWALL EXHAUST PIPE The present invention relates to fluid flow conduitsand, in particular, to a double wall exhaust pipe having integralpressure venting.

Current motor vehicles use a laminated or double wall construction forthe exhaust pipe leading from the engine to the muffler. Thisconstruction prolongs the useful life of'the pipe by providing anadditional wall thickness for reducing corrosion. It also reducesacoustical transmission or pipe noise through the walls of the pipe.Under certain conditions, pressure can build up between the walls. Thiscan cause the inner wall to collapse with a consequent reduction inengine performance. Various methods have been used for relieving thispressure buildup, usually a hole in either the inner or the outer wall.These holes leave only a single wall thickness between exhaust gas andatmosphere making the pipe locally susceptible to adverse effects fromcorrosion.

The present invention provides a double wall exhaust pipe constructionhaving integral pressure relief means and a continuous double wallthickness resistance to corrosion. More particularly, these features areachieved by forming a series of axially aligned lanced strips at spacedaxial locations along the inner wall. The strips are originally radiallyinwardly lanced and are thereafter reformed into their original positionin continuity with the wall cross section. The reforming provides acontinuous double wall between the exhaust gases and atmosphere toeliminate the localized corrosion problem above described. These lancedstrips are defined by parallel axial slits to establish pressure reliefsections which are limitedly supported only at the ends thereof. Upon apressure buildup between the walls, the strips yield inwardly to allowventing of the entrapped gases thereby preventing a collapse of theinner wall.

Accordingly, an object of the present invention is to provide a doublewall fluid flow conduit having integral pressure relief means and acontinuous double wall resistance to corrosion.

Another object of the present invention is to provide a double wallexhaust pipe for an internal combustion engine having a plurality ofin-place pressure relief sections which yield to a venting position uponpressure buildup between the walls.

A further object of the present invention is to provide a laminatedexhaust pipe construction wherein a plurality of strips are lanced inthe inner pipe and reformed to their original position to establish acontinuous double wall resistance of corrosion, the strips beinglimitedly supported only at the ends thereof and yielding inwardly torelieve pressure buildup between the inner and outer pipes.

Yet another object of the present invention is to pro vide a method ofmaking a double wall exhaust pipe with integral pressure relief meanswherein a plurality of strips are lanced at spaced axial locations alongthe length of the inner pipe and are reformed into their original crosssectional position to provide a double wall resistance to corrosionwhile being limitedly supported so as to yield to a venting positionupon a pressure buildup between the pipes.

These and other features of the present invention will be apparent toone skilled in the art upon reading the following detailed description,reference being made to the accompanying drawings showing a preferredembodiment in which:

FIG. 1 is a plan view of a motor vehicle frame incorporating an exhaustsystem for an internal combustion engine having a double wall exhaustpipe made in accordance with the present invention;

FIG. 2 is an enlarged partially sectioned fragmentary view of the doublewall exhaust pipe showing the lanced pressure relief strips;

FIG. 3 is a view taken along line 33 of FIG. 2 showing the dispositionof the in-place pressure relief strip to the conduit walls;

FIG. 4 is an enlarged fragmentary view showing the in-place pressurerelief strip with respect to the conduit walls;

FIG. 5 is a view taken along line 5-5 of FIG. 4;

FIG. 6 is a fragmentary sectional view showing the lancing of thepressure relief strip on the inner wall; and

FIG. 7 is a view taken along line 7-7 of FIG. 6 showing the lancedposition of the pressure relief strip with respect to the inner wall.

Referring to FIG. 1, there is shown a motor vehicle frame 10 in whichthere is a mounted internal combustion engine 12. For the V-type engineillustrated, exhaust manifolds 14 are provided on either side thereof.The engine exhaust gases are discharged from the exhaust manifolds 14 toan exhaust line 16 including a crossover pipe 18. The exhaust line 16includes a double wall exhaust pipe 20 serially connected to anattenuating device 22 and a tailpipe 24.

To reduce acoustical transmission through the exhaust pipe, it isconventional to use a double wall or a laminated exhaust pipeconstruction. In such a construction, a seamless or welded outer conduitis disposed tightly around a welded or seamless inner conduit. Undercertain circumstances, exhaust gases can effect a pressure buildupbetween the inner and outer conduits and cause a collapse of the innerpipe.

The present exhaust pipe includes means for preventing inner pipecollapse due to pressure buildup and maintaining a continuous doublewall resistance to corrosion. As shown in FIGS. 2 and 3, the exhaustpipe includes an outer conduit 30 defined by a cylindrical wall 31 andan inner conduit 32 defined by a cylindrical wall 33. The outer conduit30 has its inside diameter disposed tightly around the outside diameterof an inner conduit 32 in juxtaposed relationship therewith continuouslycircumferentially therearound along the axial length of the innerconduit 32. This construction provides a double thickness corrosionresistant barrier having a width 2t. To prevent pressure buildup betweenthe pipes which can cause the aforementioned collapse, an axially spacedseries of generally rectangular lanced pressure relief strips 34 areformed at spaced axial locations along the inner conduit 32. Eachpressure relief strip 34 is defined by a pair of parallel axiallyextending slits 36. It has been found that a 6 inch spacing betweenstrips having a width of 0.12 inch and a length of 0.25 inch provideseffective pressure venting capabilities. The pressure relief strips 34are supported only at bridge sections 38 adjacent the ends of the slits36. The strips, as shown in FIGS. 6 and 7, are originally radiallyinwardly lanced on the inner pipe 32 by means of a suitable tool 40. Thelancing provides a preformed strip 34a having an undulatingconfiguration along the length thereof. As shown in FIG. 7, the apex ofthe preformed strip 34a projects radially inwardly beyond the innersurface 42 of the pipe 32. This lancing may take place before or afterforming of the inner conduit 32.

As shown in FIGS. 4 and 5, the strips are thereafter reformed into crosssectional juxtaposed continuity with adjacent sections 44 of the innerpipe 32. By reforming the pressure relief strips 34 to their originalplace in the conduit cross section, a double wall corrosion resistancebarrier 21 is provided at the strip which establishes a continuousdouble wall corrosion resistance barrier along the entire axial lengthof the exhaust pipe 20.

The slits 36 establish a circumferential structural discontinuity andthe strips 34 are only limitedly supported at the bridge sections 38.Therefore, when the pressure between the inner conduit 32 and the outerconduit 30 increases beyond a predetermined value, the strip 34 willyield inwardly to allow pressure venting of the entrapped gases.

Although the strips of the preferred embodiment are defined by pairs oflances or slits, it is also apparent that reformed tabs, louvers, orother limitedly supported reformed sections in either the inner or outerconduit will provide the dual function of a continuous double wallcorrosion barrier and yielding pressure vents described above.

Although only one form of this invention has been shown and described,other forms will be readily apparent to those skilled in the art.Therefore, it is not intended to limit the scope of this invention bythe embodiment selected for the purpose of this disclosure but only bythe claims which follow.

What is claimed is:

1. A double wall exhaust pipe comprising: an inner conduit, an outerconduit surrounding said inner conduit having its inside diametertightly disposed in juxtaposed relationship with the outside diameter ofsaid inner conduit, a plurality of lanced strips on said inner conduit,each of said lanced strips including a pair of parallelcircumferentially spaced axially extending slits, said lanced stripsbeing reformed to the contour of the inside diameter of the innerconduit and being in juxtaposed relationship therewith to establish acontinuous double wall thickness resistance to corrosion, bridgesections in said inner conduit structurally supporting each of saidlanced strips adjacent the ends of said slits, said strips yieldinginwardly of said bridge sections out of juxtaposed relationship withsaid inner conduit upon a predetermined buildup of gas pressure betweenthe conduits to allow venting of the built-up gas pressure from betweenthe conduits inwardly of said inner conduit thereby to prevent pressurecollapse of said inner conduit.

2. A double wall exhaust pipe comprising: an inner conduit, an outerconduit sur rrounding said inner conduit having the inside diametertightly disposed in juxtaposed relationship with the outside diameter ofsaid inner conduit continuously circumferentially therearound to form adouble thickness wall along the entire axial length of the exhaust pipe,means forming a plurality of pressure release strips at spaced apartpoints along the length of said inner conduit, each of said strips onsaid inner conduit being located in juxtaposed relationship with saidouter conduit to form part of the double wall thickness, said stripsbeing yieldable from their juxtaposed position upon a predeterminedbuildup of gas pressure between said inner and outer conduits, and meansfor securing each end of said strips to said inner conduit to controlinwardly yielding movement of the strips to allow pressure venting ofthe entrapped gas and retention of the continuous double wall corrosionbarrier.

1. A double wall exhaust pipe comprising: an inner conduit, an outerconduit surrounding said inner conduit having its inside diametertightly disposed in juxtaposed relationship with the outside diameter ofsaid inner conduit, a plurality of lanced strips on said inner conduit,each of said lanced strips including a pair of parallelcircumferentially spaced axially extending slits, said lanced stripsbeing reformed to the contour of the inside diameter of the innerconduit and being in juxtaposed relationship therewith to establish acontinuous double wall thickness resistance to corrosion, bridgesections in said inner conduit structurally supporting each of saidlanced strips adjacent the ends of said slits, said strips yieldinginwardly of said bridge sections out of juxtaposed relationship withsaid inner conduit upon a predetermined buildup of gas pressure betweenthe conduits to allow venting of the built-up gas pressure from betweenthe conduits inwardly of said inner conduit thereby to prevent pressurecollapse of said inner conduit.
 2. A double wall exhaust pipecomprising: an inner conduit, an outer conduit surrrounding said innerconduit having the inside diameter tightly disposed in juxtaposedrelationship with the outside diameter of said inner conduitcontinuously circumferentially therearound to form a double thicknesswall along the entire axial length of the exhaust pipe, means forming aplurality of pressure release strips at spaced apart points along thelength of said inner conduit, each of said strips on said inner conduitbeing located in juxtaposed relationship with said outer conduit to formpart of the double wall thickness, said strips being yieldable fromtheir juxtaposed position upon a predetermined buildup of gas pressurebetween said inner and outer conduits, and means for securing each endof said strips to said inner conduit to control inwardly yieldingmovement of the strips to allow pressure venting of the entrapped gasand retention of the continuous double wall corrosion barrier.